Few people have seen more than one octopus in the same place at the same time—they’re usually solitary creatures, after all—but let’s suppose you did. What would you call them? Octopi? Octopuses? Perhaps octopodes? People have been quibbling over the correct plural form of octopus for well over a century, according to the Merriam-Webster dictionary, and it’s still a sore spot among word-lovers.
Quartz argues that only one way is grammatically correct—and it’s not octopi. Octopus stems from the Greek word oktopous, and technically, Greek words ending in -pus (like platypus) should be made plural by adding -podes (meaning feet) to the end. Latin words, on the other hand, are sometimes made plural with an -i ending—like stimuli and syllabi, for example.
Since the word octopus was originally Greek, it seems only logical that its plural form would be octopodes. Similarly, rhinoceros should become rhinocerotes, and stadium should become stadia. However, using these pretentious plural forms for the sake of grammatical purity would be absurd. Most words that enter English are pluralized according to the rules of English, rather than the rules of their “native form,” Merriam-Webster explains.
That leaves us with octopuses. Indeed, this form is perfectly correct, but some people still cringe when they say it. In the late 1800s, an article entitled “Octopus Philology” declared, “Some daring spirits with little Latin and less Greek rushed upon octopi; as for octopuses, a man would as soon think of swallowing one of the animals thus described as pronounce such a word at a respectable tea-table.” The article went on to recommend the use of octopods, which, fortunately, didn't stick.
However, both Merriam-Webster and the Oxford English Dictionary list octopi as an acceptable plural alongside octopuses. (Octopi is also a valid Scrabble word.) As the dictionary advises, "If you're interested in choosing the word that is most likely to be considered correct and understandable by your audience you would do well to opt for either octopuses or octopi."
So next time, go easy on the internet stranger in the comments who has just written octopuses—they're not wrong.